Skeletal muscles are complicated structures made up of at least three contractile fiber types, which differ in functional characteristics and metabolic requirements. To investigate control of microcirculation in skeletal muscles in relation to local metabolism, we are engaged in a study of the distribution of capillary blood flow to the different fiber types, and of the influence of blood flow distribution on blood tissue interchange of diffusible materials. The experimental procedures to be used include histological methods for differentiating fiber types and for identifying closed and open capillaries, as well as transport kinetic studies to evaluate capillary transport capacity, exchange and shunt flow. Our goal is an improved understanding of circulation and transport in a tissue which forms the greater part of body mass, and often (during exercise) constitutes the main load on the cardiovascular system. BIBLIOGRAPHIC REFERENCES: Gray, S. D. and Renkin, E. M. Blood supply in relation to cell metabolic type in mixed skeletal muscle. Fed. Proc. 36(3):522, 1977 Abstract. Gray, S. D. and Renkin, E. M. Distribution of capillary transit times in mammalian skeletal muscle. Proceedings XXVIIth International Congress of Physiological Sciences, Paris, 1977, in Press.